This invention relates to multihull vessels having a central section, which may be a cabin or other superstructure with or without an attached hull, and a pair of hulls or floats (hereinafter referred to as floats) oppositely spaced from the center section on pivotally mounted and joined arms or outriggers (hereinafter referred to as float arms).
In contrast to a self-righting monohull vessel which maintains stability by having its center of gravity arranged below its center of buoyancy, a multihull vessel provides buoyancy to oppose heeling in the form of divided hulls or outrigger floats. A monohull sailboat with ballasted keel has no righting moment at 0 degrees of heel where heeling moment is maximum, has maximum righting moment at 90 degrees of heel where heeling moment on the sailplan vanishes and is unstable at 180 degrees of heel. A multihull vessel has large initial stiffness or resistance to heeling due to the lateral displacement of the center of buoyancy, but the righting moment decreases as the angle of heel increases and as more of the bottom of the vessel is exposed to the forces of wind and waves and the vessel is more stable at 180 degrees of heel than at 0 degrees unless additional buoyancy is provided above the center of gravity of the upright vessel. Unless the beam of the vessel can be reduced, a very large righting moment is required, usually in the form of often unavailable external leverage, to bring the vessel back past 90 degrees of heel.
Flooding of one float is often proposed to negate the stabilizing effect of its buoyancy in the capsized position, but the disadvantages of this method are obvious, both in its performance and in subsequent recovery in a situation of continued duress. Various schemes exist to use topside buoyancy in the form of of an enlarged watertight cabin, in the form of masthead flotation or in various other forms of fixed or inflatable buoyancy on or above deck. Several applications are known in which the floats are retracted or folded to the sides of or under the center section to reduce the beam, but such methods are usually only for such purposes as preparing the vessel for trailering or for a narrower berth. Such methods cannot usually be performed with any ease while underway and external leverage is still usually required for capsize recovery. At least a couple of applications have been proposed in which the floats can be pivoted upward agaist resistance provided by resilient means to allow heeling of the center section for the primary purpose of preventing capsize. Such methods make no provision for moving the floats sufficiently inboard to make a fully capsized vessel unstable and do not provide adequate means to lift the center section of such a vessel out of or sufficiently higher in the water by such positioning of the floats.
It is believed that all of the prior art adjustable float multihull vessels are wholly dependent on concepts absent from the present invention which limit their range of applications to very few of the potential improvements in performance, safety and comfort possible as secondary benefits of the present invention. These prior art multihull vessels require float adjustability which is either too resilient or which can only assume a few rigidly supported positions, which must either be automatically actuated or which cannot be sufficiently expeditiously effected and which do not have the range and types of adjustability nor the flexibility of interaction with other rigging elements to achieve more than a few capabilities of the present invention. It is an object of the present invention to provide means for varying the positions of floats from their normal extended positions, laterally spaced from the center section to provide stability in normal sailing attitudes, to positions raised above the center section, i.e., beneath the center section when the vessel is fully capsized (the term "beneath" being used here in relation to the capsized vessel), which would render the vessel unstable in an inverted or capsized attitude, and also to positions lowered to the sides of or below the center section of the upright vessel, which would reduce the beam for various purposes such as trailering or accommodating a narrower berth.
It is another object of the invention to provide means for adjusting the floats to and maintaining them in various orientations with respect to the center section at all heights between the fully raised and the fully lowered positions, which means are contained inboard and in-place as permanent components of the structure and rigging, require no equipment to be attached to or detached from the floats or arms to effect the adjustments and require no releasable restraints and a minimum of fixed limits on the rotation around joints within the float arms. Applications in addition to those alluded to above for reducing the beam in the extreme positions include alterations in float height, distance from the center hull and attitude for fine adjustments to the vessel's performance in different operational circumstances and for more fundamental adjustments of the vessel's performance characteristics such as lifting the main hull of a trimaran nearly clear of the water to gain any performance advantages of a catamaran or rotating the floats to bring planing or hydrofoil surfaces into operational positions.
It is a further object of the invention to make elements of the standing rigging adjustable such that the position of a mast may be varied from fully vertical to fully horizontal (possibly in either the fore or aft directions) and such that adjustments of the mast can be carried out in a variety of ways, independently of or in conjunction with adjustments of the floats. Beside independent lowering of the mast for stowage and raising of the mast from the stowed position, the applications include lowering the mast as the floats are raised in a capsize recovery for the purpose of pivoting shrouds out of the way of the floats; lowering the mast to the deck in a capsize recovery for the purpose of utilizing shrouds to lift the floats, with motive force possibly being supplied by masthead flotation; causing the mast to be re-raised during capsize recovery by the re-lowering of the floats and leaving the mast stowed on the deck as floats are re-lowered during capsize recovery, with raising and lowering referred to the vessel in its upright position.
It is a further object of the invention to bring control of rigging or other equipment which effects and maintains the adjustment of floats and mast to a central location where this control can be readily and selectably exercised in a variety of combinations of possible operations by the crew while underway or even while capsized.
It should be noted that in all of the following description terms such as "up" and "down" or "raising" and "lowering" will be assumed to be defined in terms of the upright vessel, unless otherwise noted, even when it is being considered to be upside down in the water.